Seals for electrical devices

ABSTRACT

A pinched seal for envelopes of electrical devices having a plurality of lead-in conductors, in which a layer of material of lower softening point than the envelope is placed between foil portions of the lead-in conductors to form a sandwich so that during the formation of the pinched-seal the material between the foils flows as readily as the material outside the foils even though it is at a lower temperature.

United States Patent Inventors Appl. No.

Filed Patented Assignee Priority SEALS FOR ELECTRICAL DEVICES 12 Claims, 4 Drawing Figs.

US. Cl 174/50.62, 313/317, 313/332 Int. Cl H0lj 5/38 [50] Field of Search 313/274, 317, 318, 332; 174/5064 [56] References Cited UNITED STATES PATENTS 1,271,245 7/1918 Reckinghausen 174/5064 X FOREIGN PATENTS 610,933 10/1948 Great Britain 174/5064 Primary ExaminerDarrell L. Clay Attorney-Laurence Burns ABSTRACT: A pinched seal for envelopes of electrical devices having a plurality of leadin conductors, in which a layer of material of lower softening point than the envelope is placed between foil portions of the lead-in conductors to form a sandwich so that during the formation of the pinched'seal the material between the foils flows as readily as the material outside the foils even though it is at a lower temperature.

PATENT-EU sEP28 IHYI 7 3,609,212

PRIQRARTFigJ. 13 13 JOHN WILLOUGHBY THOMAS WRIGHT FRANK LEWIS ATTORNEY SEALS FOR ELECTRICAL DEVICES The present invention relates to improvements in seals for electrical devices such as lamps.

The envelopes of tungsten-halogen lamps are usually sealed by heating and pressing together the walls of the glass envelope around a lead. The envelope is usually made of fused quartz. To form a hermetic seal which is satisfactory at the operating temperature of the lamp the lead includes a foil of molydenum whose thermal expansion characteristics match those of the quartz forming the envelope. Such a seal is known as a pinch seal."

In lamps designed to operate at high power, it is desirable to have a plurality of foils sealed in each neck to carry high currents to the filament.

According to the present invention, a seal for an electric device comprises an envelope and a plurality of lead-in conductors sealed in and extending through a flattened neck of the envelope, the lead-in conductors having foil portions which are arranged in layered array, adjacent foils of the array being separated by material which has a melting point lower than that of the material of the neck of the envelope and the foils being hermetically sealed between the neck of the envelope and the material of lower melting point.

Thus a seal may be made by placing in the neck of an envelope foil portions interleaved with material of lower melting point than the material of the neck of the envelope and heating and pinching together the neck to form a hermetic seal. The material of lower melting point is at a lower temperature than the neck during pinching but its lower melting point ensures that the viscosities of the said material and the material of the neck are similar so that the flow of material round the foil portions is even and a complete seal is made. In preferred forms the foil portions are interleaved with pieces of material having approximately the same area as the foil portions.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings of which:

FIG. 1 shows fragmentary front and side elevations of a known pinch-sealed lamp,

FIG. 2 shows fragmentary front and side elevations of a first pinch-sealed lamp according to the invention,

FIG. 3 shows fragmentary front and side elevations of a second pinch-sealed lamp according to the invention, and

FIG. 4 shows fragmentary front and side elevations of a third pinch-seal lamp according to the invention.

Referring to FIG. 1, this shows a fragment of a tungstenhalogen lamp with a seal of known construction. A fused quartz envelope 11 has a flattened neck portion 12. Fused quartz and fused silica are synonymous terms for silicon dioxide in the glassy state. A tungsten filament 13 is welded to a molybdenum foil 14 of a lead-in conductor. Both sides of a loop of platinum-coated molybdenum wire 15 are welded to the foil 14. The flattened neck portion is heated and pinched around the foil to form a hermetic seal. The tungsten filament 13 extends into the interior of the glass envelope and the loop of wire extends to the exterior. As it is the looped portion of the wire that is exposed to the exterior, there are no cut ends and thus the molybdenum is not exposed.

It is desirable to make foil seals capable of carrying high currents, thereby permitting the manufacture of tungstenhalogen lamps which can operate at high power. While it is possible to make seals having a plurality of foils with quartz envelopes it has proved to be extremely difficult in practice. There is a difference in the viscosity of the quartz in the pinch during the pinching operationass the quartz between the foils remains cooler and therefore more viscous than the quartz at the outside of the pinch. This makes it difficult to obtain a perfect seal.

Referring to FIG. 2, this shows a seal for a tungsten-halogen lamp according to the invention. A quartz envelope [6 has a flattened neck portion 17. A loop of tungsten wire 18 for connection to the filament of the lamp is welded at its ends to two molybdenum foils 19. A loop of molybdenum wire 20 coated with platinum is welded at its ends to the two foils the loop of wire 18, the two foils l9 and the loop of wire 20 form two lead-in conductors connected in parallel. A piece of quartz glass 21 having a composition of 96 percent silica and 4 percent alkali borates such is sold under the Reg. Trade Mark Vycor, extending for the same areas as the foils before pinching is sandwiched between the two foils 19. The flattened neck portion 17 is pinched around the foils I9 and Vycor glass 21 to form a hermetically sealed joint. Vycor glass has a melting point which is lower than that of pure quartz. Therefore, during the heating and pinching operation, although the glass between the foils I9 is at a lower temperature than the quartz of the neck portion it has a similar viscosi' ty, which results in an even flowing of the glass and quartz round the foils and a complete seal. By looping the wire 20 the platinum coating is not broken and the molybdenum core is not exposed to the air.

FIGS. 3 and 4 show two more alternative embodiments of the invention similar to the embodiment of FIG. 2. The corresponding parts are given the same numerals. In the embodiment of FIG. 3 two sets of foils 19' and 19" are pinch-sealed in the neck portion 17. The foils of each set are separated by pieces of Vycor glass 21' and 21" respectively.

In the embodiment of FIG. 4, there are three foils 19" separated by two pieces of Vycor glass 21". The foils are connected in parallel by a looped tungsten wire 18" and a tungsten wire 22 welded to it on the inside and a looped platinumcoated molybdenum wire 20" and a platinumcoated molybdenum wire 23 welded to it on the exterior.

The seals of FIGS. 3 and 4 are formed in a similar manner to that of FIG. 2. By having more foils in parallel higher currents can be taken.

Other silica or quartz glasses may be used instead of Vycor. Silica or quartz glasses generally consist of more then 10 percent fused quartz and have a softening point l00-200 C. lower than pure silica. They must, however, be compatible with fused quartz and form a satisfactory seal with molybdenum.

What we claim is:

1. In an envelope for an electric device a seal comprising:

a pinched portion of the envelope;

a plurality of lead-in conductors extending through the pinched portion, having metal foil portions which are arranged in layered array;

and an insulating material which separates adjacent foil portions of the array and which has a lower softening point than the material of the pinched portion of the envelope. the foil portions being hermetically sealed between the pinched portion and the material of lower softening point.

2. A seal as claimed in claim I wherein the pinched portion is of fused quartz.

3. A seal as claimed in claim 1 wherein the material of lower melting point is silica glass.

'4. A seal as claimed in claim 3 wherein the silica glass has a composition of 96 percent silica and 4 percent alkali borates.

5. A seal as claimed in claim 1, wherein the foil portions are of molybdenum.

6. A seal as claimed in claim I and including a looped conductor and two foil portions being interconnected outside the envelope by the looped conductor.

7. A seal as claimed in claim 6 wherein the looped conductor is welded to the two foil portions at its two ends.

8. A seal as claimed in claim 6 wherein the looped conductor is a platinum-coated molybdenum wire.

9. A seal as claimed in claim 1 and including a looped conductor and two foil portions being interconnected inside the envelope by the looped conductor.

10. A seal as claimed in claim 9 wherein the looped conductor is welded at its two ends to the two foil portions.

11. A seal as claimed in claim 9 wherein the looped conductor is a tungsten wire.

12. A seal as claimed in claim 11 wherein another foil portion is disposed between the two foil portions and separated tions the conductors being joined to the two looped conductors outside the envelope and inside the envelope respectively. 

1. In an envelope for an electric device a seal comprising: a pinched portion of the envelope; a plurality of lead-in conductors extending through the pinched portion, having metal foil portions which are arranged in layered array; and an insulating material which separates adjacent foil portions of the array and which has a lower softening point than the material of the pinched portion of the envelope, the foil portions being hermetically sealed between the pinched portion and the material of lower softening point.
 2. A seal as claimed in claim 1 wherein the pinchEd portion is of fused quartz.
 3. A seal as claimed in claim 1 wherein the material of lower melting point is silica glass.
 4. A seal as claimed in claim 3 wherein the silica glass has a composition of 96 percent silica and 4 percent alkali borates.
 5. A seal as claimed in claim 1, wherein the foil portions are of molybdenum.
 6. A seal as claimed in claim 1 and including a looped conductor and two foil portions being interconnected outside the envelope by the looped conductor.
 7. A seal as claimed in claim 6 wherein the looped conductor is welded to the two foil portions at its two ends.
 8. A seal as claimed in claim 6 wherein the looped conductor is a platinum-coated molybdenum wire.
 9. A seal as claimed in claim 1 and including a looped conductor and two foil portions being interconnected inside the envelope by the looped conductor.
 10. A seal as claimed in claim 9 wherein the looped conductor is welded at its two ends to the two foil portions.
 11. A seal as claimed in claim 9 wherein the looped conductor is a tungsten wire.
 12. A seal as claimed in claim 11 wherein another foil portion is disposed between the two foil portions and separated from them by layers of the material of lower softening point and an additional looped conductor in which said conductors connect the said first portion in parallel which the two foil portions the conductors being joined to the two looped conductors outside the envelope and inside the envelope respectively. 